Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

515
FXUS63 KLOT 141750
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1250 PM CDT Tue Jul 14 2026

.KEY MESSAGES...

- Hot conditions are expected for much of the week; though
  somewhat cooler near Lake Michigan.

&&

.DISCUSSION...
Issued at 135 AM CDT Tue Jul 14 2026

The core of a sprawling mid-level ridge will expand east and
build farther across the region today. Thicknesses will
increase, supporting a several degree jump in high temperatures
compared to yesterday, with upper 90 degree readings in play in
and around the more deeply-mixed urban Chicago corridor
(including Midway and O`Hare). Based on observed dewpoint trends
on Monday, guidance with the strongest PBL mixing schemes (RAP
and HRRR) where too deeply mixed, with notable dry biases during
the afternoon, while the NAM/NAMNest/NSSL WRF were all a bit
too moist. The ECMWF seems to have handled trends the best
across the deterministic guidance suite, and have commensurately
weighted the latest dewpoint forecast towards the EC solution.
This results in dewpoints generally in the low 70s today away
from the Chicago core, and this tracks with the idea of somewhat
increased evapotranspiration (ET) effects as the surface high
builds a bit farther eastward. Peak heat indices will likely be
near 100 degrees (locally higher or lower due to proximity to
agricultural areas and enhanced ET).

Air temperatures will likely be similar on Tuesday. Dewpoints
may tick up a few degrees as the low-level moisture profile is
forecast to deepen ever so slightly. It still looks like the
NAM remains a bit too moist/undermixed with dewpoints in the mid
to upper 70s, with low to locally mid 70s values looking more
appropriate given the lack of moist Gulf trajectories. Heat
indices are forecast to once again largely top out around 100
degrees, but with the slight increase in dewpoints, could end up
seeing more in the way of a smattering of 105 degree readings.
If this outcome becomes more apparent and widespread, a Heat
Advisory could be needed. At this time, coverage and confidence
in 105+ values remains too low/limited to justify an advisory.

By Thursday, the upper ridge will begin to break down and
weaken as synoptic troughing amplifies across eastern Canada. As
a result, highs will likely come down a few degrees, but low-
level moisture will remain in place. Guidance which had
previously advertised a lake-enhanced backdoor front rolling
through northeast Illinois and northwest Indiana have all backed
off on this, with a trend towards a stronger high/ridge axis
overhead. It still looks like we`ll get a stronger lake
breeze/northeast push off the lake, but this may not be until
late in the day after peak heating.

This trend brings the potential for one of the three Extreme
Heat Warning criteria for Cook County/Chicago (three days of
100-105 heat indices) more into play. Am confident in peak
values around 100 today and Wednesday away from the immediate
lake influence (more than about a mile to two inland), but
whether we see a full third day of solidly 100+ values does
still remain unclear, particularly given the potential for
temperatures to come down a degree or three. Additionally, this
heat episode just doesn`t seem to be to the same caliber as the
event leading up to Independence Day. I ultimately would like to
see a more significant spatiotemporal extent of solidly 100-105
readings to justify hoisting the highest level heat product we
have. Given this, and overnight temperatures forecast to dip
into the mid 70s, decided to hold off on issuing an Extreme
Heat Warning for Chicago/Cook county on this shift, but did
give this consideration. If confidence in 100+ heat indices
increases for Thursday and peak values increase further for
Wednesday, can`t discount the need for a Warning.

Regarding lake cooling: based on how temperatures have behaved
the last few days, any cooler temperatures will be confined to
the immediate lakefront, with conditions warming quickly more
than one mile inland. The lake breeze pushes will be directed
mostly into Lake County IL, and as such, the lake cooling
presence will be even further muted across Lake and Porter
counties in northwest Indiana.

Additionally for Thursday, can`t entirely rule out some isolated
afternoon thunderstorms, particularly in the vicinity of the
inland-advancing lake breeze. Forecast sounding still generally
looked capped, although not as capped as today and Wednesday.
Capped any PoP mentions to slight chance, and suspect things
will largely remain dry, but the presence of somewhat deeper
moisture does support the potential for some airmass convection
in the region.

Finally: numerous wildfires are evident across southwestern
Ontario. Associated smoke is largely forecast to remain north of
us and aloft through tonight. However, as low to mid-level flow
turns more north to northwesterly on Wednesday, there is some
potential smoke builds southward towards our region, particularly
beyond Wednesday night (per the latest HRRR SMOKE output). No
mention of smoke or manually-increased cloud cover yet, but
something we`ll need to keep an eye on over the coming forecast
cycles.

Boundary layer moisture will increase further on Friday and
coupled with a weak mid-level wave to our west, could result in
scattered afternoon showers and thunderstorms. Very little flow
in the column will support slow-moving storms capable of brief
locally heavy rainfall and perhaps a gusty downburst wind
threat. A series of more pronounced waves will scoot to our
north and northeast Saturday into Sunday which will keep at
least some low-end storm chances running through the weekend and
into early next week.

Carlaw


.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1250 PM CDT Tue Jul 14 2026

- Light east wind shifts with the lake breeze at ORD/MDW each
  afternoon

Main concern through the period is the timing of weak lake
breezes at MDW/ORD this afternoon and again Wednesday afternoon.
Have slowed the arrival of the lake breeze this afternoon in the
TAFs by an hour, 19Z MDW and 20Z ORD, though given the very
weak surface flow will have to monitor observational trends for
any surges or stalling of the boundary over the next few hours.
Speeds are expected to remain light but can`t rule out a brief
period of speeds around 7-9 kt with the initial wind shift.
Winds then return to a west direction later this evening
through early Wednesday afternoon before another lake breeze
turns winds east at ORD/MDW/GYY. Farther inland (DPA/RFD)
expect light west to at times variable winds through the
period.

VFR conditions are currently forecast with some passing high
cirrus and a thin smoke layer aloft possible at times. Can`t
rule out shallow ground fog/BR out toward RFD early Wednesday
morning but confidence is not high enough to include with this
update. Surface visibility reductions due to smoke will also
need to be monitored toward the end of just beyond the current
30-hr TAF period.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Air Quality Alert until midnight CDT Wednesday night for
     ILZ005-ILZ006-ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-
     ILZ105-ILZ106-ILZ107-ILZ108.

IN...Air Quality Alert until midnight CDT Wednesday night for
     INZ001-INZ002-INZ010-INZ011.

     Air Quality Alert from midnight tonight to 1 AM EDT Thursday
     for INZ019.

LM...None.

&&

$$

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